1. Field of the Invention
The present invention relates to a disc recognizing method for recognizing the type of disc seated in an optical disc playback apparatus, and more particularly to a disc recognizing method which can prevent the deformation of a leaf spring used to support a pickup associated with the playback apparatus.
2. Description of the Related Art
Generally, optical disc playback apparatuses employ an optical disc as a recording medium, and are classified into compact disc playback apparatuses and laser disc playback apparatuses in accordance with the size of the disc utilized therewith. Recently, optical disc playback apparatuses capable of reproducing information recorded on different sized optical disc have been developed. Such a device controls the playback of a seated disc by utilizing a plurality of switches for detecting the starting point of recorded data.
In more detail, as illustrated in FIG. 1, first starting point detecting switch 7, which is adjacent to a turntable 2, and second starting point detecting switch 8 are utilized for detecting different playback starting points in accordance with the size of a disc 1. Then, playback is carried out, in accordance with the detection of the starting point corresponding to a compact disc or laser disc, for example. First starting point detecting switch 7 is installed at a position which corresponds to the starting point of a compact disc (or some other disc having the same playback starting point, i.e., the location of a leading area, as a compact disc), and the second starting point detecting switch 8 is installed at a position which corresponds to the starting point of a laser disc (or a disc with the same playback point as a laser disc).
FIG. 2 is a flowchart illustrating a conventional disc recognizing method which is briefly described below with reference to FIGS. 1 and 2. If an optical disc playback apparatus is set to a playback mode, according to a user-designated control command or input information, a drive device (not shown) moves pickup 3 to a home position which is outward from second starting point detecting switch 8 with respect to a radial direction of disc 1 (step 11). When pickup 3 is at the home position, system controller 12 controls the drive device to move pickup 3 inwardly with respect to the radial direction of the disc (step 12). Then, as pickup 3 passes second starting point detecting switch 8, this switch is turned "ON" (step 13). (Here, first and second starting point detecting switches 7 and 8 are also called "limit switches" since they inhibit pickup 3 from traveling further toward the inner circumference of the disc.) Pickup 3 stops, when system controller 12 determines that second starting point detecting switch 8 is "ON", and a focusing operation is attempted (step 15).
When the light reflected off of disc 1 during a focusing operation exceeds a predetermined level, it is determined that a focus-lock condition is obtained. At this time, in the absence of a disc, the reflected light would be below the predetermined level because no light is reflected. Accordingly, the focus-lock condition, or lack thereof, can be used to determine the presence or absence of a disc.
When the focus-lock condition is detected in step 16, pickup 3 detects the extent to which disc 1 is warped, in accordance the level of light received during the focusing operation. The disc may be warped due to its own weight, or due to the internal heat of the playback apparatus. The center of the disc is fixed to turntable 2 by a clamp (not illustrated). Accordingly, there is no warp in the disc at the center and the warp increases toward the circumference of the disc.
If disc 1 is not warped, the playback is performed normally. Whereas if disc 1 is warped, system controller 12 commands servo 11 to supply a tilt value signal based upon the level of reflected light, which depends on the distance between a surface of disc 1 and pickup 3, to tilt driver 9. Tilt driver 9 is activated in response to a signal from servo 11 at the moment of a focus-lock, and vertically adjusts pickup transfer 6, by causing pickup transfer 6 to pivot about a point which is located proximate the center of disc 1, in response to the tilt value supplied from servo 11, to compensate for the warp of the disc. As shown in FIG. 1, if the tilt value is the distance indicated by L, tilt driver 9 moves pickup transfer 6 downward from its original position 6' (denoted by the dotted line in FIG. 1). After pickup transfer 6 is adjusted by tilt driver 9, ordinary focusing and playback operations continue (step 17).
However, if it is determined that a focus-lock condition does not exist in step 16, focusing is again attempted and the focus-lock is checked (step 18). At this time, if focus-lock is accomplished by the refocusing attempt, the above-described step 17 is executed. However, if the focus-lock condition is not obtained in step 18, disc 1 is determined to not be present at the position of second starting point detecting switch 8 and focusing operations are terminated (step 19). In such a case, pickup 3 is transferred inwardly by the drive device. When pickup 3 reaches first starting point detecting switch 7, the controlling of the focusing is carried out in a manner similar to the method described above (steps 20 and 24). Since the frequency of warping of a compact disc tends to be less than that of a laser disc, after a previously reproduced laser disc is removed, pickup transfer 6 is in a tilted condition to compensate for warpage of the previously used laser disc.
When information recorded on a laser disc is subsequently reproduced, pickup transfer 6 is once again adjusted by controlling the operation of servo 11 and tilting driver 9 when pickup 3 reaches second starting point detecting switch 8, in the manner described above. Thus, normal playback is carried out without difficulty. However, as shown in FIG. 1, if a compact disc is reproduced, pickup 3 must be transferred to a position proximate first starting point detecting switch 7 while transfer device 6 is under a tilted condition. However, if first starting point detecting switch 7 is close to turntable 2 (such positioning is ordinarily required for playback of compact discs), portions of pickup 3 may come into contact with turntable 2 in the area indicated at A, and thus leaf spring 4, which supports optical elements of pickup 3, becomes deformed. At this time, minor deformation of leaf spring 4 merely results in a slightly longer time than normal for reading out information from the read-in area because of potential errors in focusing and tracking operations due to the improper position of elements supported by lead spring 4. However, severe deformation of the leaf spring inhibits playback or conversion from video to audio, and vice versa, in a compact disc which has both video and audio signals recorded thereon, because errors may occur in reading positional information relating to the various signals. Moreover, if a laser disc is reproduced while leaf spring 4 is in a deformed state, noise such as longitudinal and traversal lines will appear in the resulting picture because optical elements, including objective lens 5, which are supported by leaf spring 4, may not be properly positioned.